Generally speaking, there will be rails at both sides of a rack and the rails are provided for the user to open the drawers at the rack. In order to reduce costs, a common rail is to utilize a long strip bending with two parallel boards, one of which is used for a drawer to be disposed against. However, while the cost of the common rail is low, the drawer may fall when there is excessive force applied on it, which is not only inconvenient, but also increasing the possibility to cause injury to the user. Thus, some rails will be equipped with a circular bumps or tapered protrusions to prevent the drawer from falling off due to excessive force applied thereon. However, the common rail may be disadvantageous because the round bumps or tapered protrusion may still be removed due to excessive force. If the number of the round bumps or tapered protrusions are increased, the drawer is hard to be removed. Therefore, there remains a need for a new and improved structure to prevent the drawer from falling off.